A ceramic block with a built in electrode has a flat bearing surface in which a glass substrate is mounted for a semiconductor wafer or LCD (liquid crystal display). The ceramic block is formed by firing laminated insulation ceramic sheets. A sheet electrode spreading out parallel to the bearing surface is fitted between the laminated ceramic sheets. The sheet electrode may be the form of a metallized layer plated on a film, mesh or ceramic sheet. Normally, a hole extending from the opposite side of the bearing surface to the sheet electrode is provided in the ceramic block. A drawn out conductor for supplying voltage to the sheet electrode passes through the hole and connects to an external electrode of the ceramic block.
Japanese patent Publication No. 62-264638 discloses an electrostatic chuck platform, as a ceramic block with a built in electrode. An insertion hole is formed in the electrostatic chuck platform, on the opposite side to the bearing surface, and an external electrode is fixed into the insertion hole. A plurality of connector holes connecting a sheet electrode with the insertion hole are formed, and conductive paste is filled into the connector holes. Voltage is applied through the external electrode and the conductive paste.
Japanese patent Publication No. 2001-296269 discloses a ceramic heater for an oxygen sensor, as a ceramic block with a built in electrode. The ceramic heater has a resistance heating element patter, as a sheet electrode, and a plurality of ceramic insulating layers. A number of through holes having a metallic film plated on an inner surface are formed in the ceramic heater. A number of electrode terminal sections are exposed on an outer surface of the ceramic insulation layer, and pass through the through holes to extend towards the electrodes. Plate shaped conductors (lead lines) are pressure bonded to the exposed electrode terminal sections using a ring clasp.
Japanese patent Publication No. 2000-106391 discloses an insulating ceramic base for a susceptor for supporting a semiconductor, as a ceramic block with a built in electrode. A locating hole is formed in the ceramic base, at an opposite side to the bearing surface. Part of a mesh electrode within the ceramic base is exposed to the bottom of the locating hole. A terminal for supplying voltage to the mesh electrode is located in the locating hole. Before heat treatment of the ceramic base, an intermediate material is provided between the bottom of the locating hole and the terminal. The intermediate material is composed of a conductive metal matrix-ceramics complex, and is fused by heat treatment of the ceramic base. As a result, the terminal is electrically connected to the mesh electrode, and joined to the ceramic base.
Japanese patent Publication No. 2003-115529 discloses an electrostatic chuck unit, as a ceramic block with a built in electrode. The electrostatic chuck unit comprises insulating layers where the bearing surface is formed, and a conductive layer which spreads across the insulating layers, namely an electrode. The insulating layers are laminated on a metal foundation formed with a through hole. An insulating member is provided in the through hole, and a guide hole is formed in the insulating member. A conductor extends within the guide hole, with one end of the conductor being fixed to the conductive layer with solder, and the other end being fixed to a feed terminal with solder.
In order to improve the adsorption force of the electrostatic chuck and the thermal responsiveness of the ceramic heater, it is preferable to make the distance from the bearing surface to the sheet electrode smaller. Generally, a ceramic sheet where a bearing surface is formed has a thickness of 50-500 μm taking into consideration dielectric strength and mechanical strength. The ceramic sheet and the sheet electrode are different in their coefficients of thermal expansion and thermal contraction, respectively. Therefore, high residual stress arises at connecting sections of the sheet electrode and the drawn out conductor and it becomes easy for cracking to arise in the thin ceramic sheet and the sheet electrode.
It is desirable to provide a ceramic block with a built in electrode whereby it is difficult for cracking to arise in a thin ceramic sheet where a bearing surface is formed and in a sheet electrode, and also to provide a manufacturing method for such a ceramic block.